Standardized on using CMAKE_CXX_STANDARD to control the cxx_std_ used.

Author: robertosfield

CMakeLists.txt

@@ -90,9 +90,6 @@ if (VSG_SUPPORTS_Windowing)
     endif()
 endif()
 
-set(VSG_CXX_TARGET 17 CACHE STRING "Set target C++ standard version, valid values are 17, 20 & 23")
-
-
 option(VSG_USE_dynamic_cast "Use dynamic_cast in vsg::Object::cast<T>(), default is OFF and uses VSG native casting which provides 2-3x faster than using dynamic_cast<>." OFF)
 
 # this line needs to be after the call to setup_build_vars()

src/vsg/CMakeLists.txt

@@ -412,15 +412,20 @@ set_property(TARGET vsg PROPERTY VERSION ${VSG_VERSION_MAJOR}.${VSG_VERSION_MINO
 set_property(TARGET vsg PROPERTY SOVERSION ${VSG_SOVERSION})
 set_property(TARGET vsg PROPERTY POSITION_INDEPENDENT_CODE ON)
 
-if (VSG_CXX_TARGET EQUAL 23)
-    target_compile_features(vsg PUBLIC cxx_std_23)
-elseif (VSG_CXX_TARGET EQUAL 20)
-    target_compile_features(vsg PUBLIC cxx_std_20)
-elseif (VSG_CXX_TARGET EQUAL 17)
+# set up the C++ Standard used
+if (NOT CMAKE_CXX_STANDARD)
+    # no CMAKE_CXX_STANDARD explicitly defined so default to 17
     target_compile_features(vsg PUBLIC cxx_std_17)
-else()
-    message("Warning: invalid VSG_CXX_TARGET setting of " ${VSG_CXX_TARGET} " valid settings are 17, 20 or 23")
+elseif (${CMAKE_CXX_STANDARD} EQUAL 17)
     target_compile_features(vsg PUBLIC cxx_std_17)
+elseif (${CMAKE_CXX_STANDARD} EQUAL 20)
+    target_compile_features(vsg PUBLIC cxx_std_20) # CMake minimum version 3.12
+elseif (${CMAKE_CXX_STANDARD} EQUAL 23)
+    target_compile_features(vsg PUBLIC cxx_std_23) # CMake minimum version 3.20
+elseif (${CMAKE_CXX_STANDARD} EQUAL 26)
+    target_compile_features(vsg PUBLIC cxx_std_26) # CMake minimum version 3.30
+else()
+    message(FATAL_ERROR "Invalid CMAKE_CXX_STANDARD value of " ${CMAKE_CXX_STANDARD} ", supported values are 17, 20 or 23.")
 endif()